Extractive separation of rare earth ions by using calix[4]arene with isopropyl hydrogen phosphonate at upper rim

5,11,17,23-Tetrakis(isopropyl hydrogen phosphonomethyl)- 25,26,27,28 - tetrapropoxycalix[4]arene in cone conformation has been synthesized to investigate extraction behavior for nine trivalent rare earth metal ions from chloride media into chloroform, together with isopropyl hydrogen (4-propoxyphenyl)methylphosphonate as a corresponding monomer. Although the aqueous distributions of the present extractants were greater than those of butyl ester type of the previous extractants, they were trace and slight amounts under the experimental condition for calix[4]arene and monomeric derivatives, respectively. From the result of pH dependency, extraction takes place by a simple ion-exchange mechanism for both extractants. The extraction ability between the present extractants for rare earth ions was comparable. Results of a Job plot and a loading test indicate that for calix[4]arene derivative, stoichiometry of the extraction is 1:1. The separation efficiency of a calix[4]arene derivative is less than that of a monomeric derivative. It is attributed to the offset by the size effect of a coordination site at the larger upper rim of calix[4]arene (for relatively larger light rare earth ions) and strong affinity of phosphonate group to heavy rare earth ions. Such result is similar to that of derivatives with butyl ester.